Method for making lithium aluminide compound in atmospheric environment

ABSTRACT

A method for making lithium aluminide compound in atmospheric environment at a working temperature includes accomplishing a diffusive electrolysis in an electrolyte composed of lithium chloride, potassium chloride and calcium chloride, exerting a direct current (voltage) on the electrolyte to reduce the lithium ions into lithium atoms on the surface of an rotative aluminum cathode, and subsequently the lithium atoms diffusing into the aluminum cathode during the electrolysis.

RELATED APPLICATIONS

The application claims priority to Taiwan Application Serial Number 96110901, filed Mar. 28, 2007, which is herein incorporated by reference.

BACKGROUND

1. Field of Invention

The present invention relates to a method for making lithium aluminide (AlLi) compound. More particularly, the present invention relates to a method for making lithium aluminide compound in an atmospheric environment.

2. Description of Related Art

The application of the lithium aluminide compound is limited because the ingredients of the lithium aluminide compound are difficult to control. Conventionally, the intermetallic FeLi compound or intermetallic CuLi compound is prepared by a ball-grinding method in a chamber with a protective gaseous environment. The ball-grinding method consumes a lot of energy resources and time. The ball grinding process forces the metal powder blend into the lithium granule by mechanical metallurgy. However, in the case of lithium aluminide compound, both the aluminum powder and solid lithium are extremely unstable in air, so that the ball grinding process is not adequate for the preparation of the lithium aluminide compound.

The conventional lithium aluminide compound is prepared by putting solid lithium into an aluminum melt under a layer of flux or in an argon atmosphere. The above process gets even more complicated with increasing lithium content in the aluminum alloy melt. Moreover, solid lithium is extremely unstable in air because of the air humidity may result in dangerous flash lithium gasification. A high-frequency induction furnace or a closed electrical furnaces is needed to melt aluminum-lithium, surrounding the melt with a protective gas, argon. Therefore, the conventional process of preparing a lithium-containing alloy is not only difficult to operate but also expensive.

Solid lithium is very dangerous during the hauling and storage period, and the cost cannot be lowered in regions without lithium ore that relies on importing the lithium from the place of origin.

SUMMARY

A method for making lithium aluminide (AlLi) compound in an atmospheric environment in accordance with the present invention satisfies the need to lower the danger of conventional processes and the cost of storing and transporting the solid lithium.

The method comprises employing an aluminum material as a cathode and dipping the aluminum cathode into an electrolyte composed of lithium chloride and potassium chloride. Exerting a direct current (a voltage) to the electrolyte to decompose the lithium chloride in the electrolyte and to reduce the lithium ion on the aluminum cathode at a working temperature, and diffusing the lithium atoms into the aluminum cathode to obtain a lithium aluminide compound. During the electrolysis, the aluminum cathode can be rotated slowly with a predetermined rotating speed, which is controlled under 60 rpm. The component of the electrolyte, lithium chloride (LiCl), provides the lithium source for making the lithium aluminide compound, and potassium chloride (KCL) is employed as a flux to reduce the temperature and improve the flowability of the electrolyte. The lithium material is diffused into the aluminum cathode by a diffusive electrolysis process. The interaction between the lithium and the aluminum in the electrolyte is shown as follow:

Anode: 2Cl⁻→Cl₂+2e ⁻

Cathode: Li⁺ +e ⁻→Li

The diffusive electrolysis may proceed in an atmospheric environment to form a lithium aluminide compound within the range of Al-2 wt. % Li˜Al-50 wt. % Li, that is, the lithium concentration of the lithium aluminide compound is within the range of 2˜50% by weight. Due to the poor affinity between the potassium, calcium and the aluminum cathode, the lithium aluminide compound contains less than 50 ppm of potassium and calcium. Sodium is a very common impurity in chloride salt and the lithium aluminide compound contains less than 30 ppm of sodium.

In conclusion, the embodiment of the present invention provides a safer and easier way to prepare lithium aluminide compound. The method employing the aluminum material as a cathode and dipping the aluminum cathode into the electrolyte composed of lithium chloride and potassium chloride. The lithium ions of the electrolyte are reduced into Li atoms on AL cathode. The lithium atoms simultaneously diffused into the aluminum cathode under a direct current at a working temperature. The embodiment of the present invention provides a safer and more convenient way to transport and store the lithium raw material by employing the lithium chloride, a stable chemical in atmospheric environment, as the raw material of the lithium aluminide compound.

It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 is a flowchart of steps in accordance with an embodiment of the present invention;

FIG. 2 is an operational cross-section view of a specific electrolytic bath when the diffusive electrolysis is in progress therein; and

FIG. 3 is a sketch of X-ray crystal structures of an aluminum sheet before and after a diffusive electrolysis treatment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

Refer to FIG. 1. FIG. 1 is a flowchart of steps in accordance with an embodiment of the present invention. The steps of the embodiment include providing an electrolytic bath with an electrolyte composed of lithium chloride and potassium chloride. Employing an aluminum material as a cathode and dipping the aluminum cathode into the electrolyte. Exerting a direct current (voltage) to the electrolyte to move the lithium ion in the electrolyte toward the aluminum cathode at a working temperature. The lithium ions were reduced into lithium atoms, diffusing the lithium into the aluminum cathode to obtain a lithium aluminide compound.

Refer to FIG. 2. FIG. 2 is an operational cross-section view of a specific electrolytic bath when the diffusive electrolysis is in progress therein. An electrolyte 241 is loaded into a container 230 in an atmospheric environment. In accordance with an embodiment of the invention, the electrolyte 241 essentially consists of 25˜45% by weight (wt. %) of lithium chloride, 30˜60% by weight of potassium chloride, and at least 5 wt. % by weight of calcium chloride.

The electrolysis facility 200 possess a double-decked structure, which comprises an external furnace 210, an alumina inner 220, and a lid 211 covered on the top of external furnace 210.

A plank 221 is set in the bottom of the alumina inner 220, and a container 230 is mounted on the plank 221 wherein the container 230 is a steel-made container to load the electrolyte 241.

A heater 250, a thermocouple 260, an anode 242 and a cathode 243 are placed in the container 230, wherein the heater 250 to heat the electrolyte 241 and the thermocouple 260 is dipped in the electrolyte 241 to monitor the variation of temperature in the electrolytic system.

Portions of the anode 242 and a cathode 243 are dipped into the electrolyte 241. A cathode rotating member 244 and cathode rotating member 245 rotates the cathode 243 in a predetermined speed. In accordance with an embodiment of the invention, an aluminum material is used as the cathode 243 and the material of the anode 242 comprises graphite, polymer or alloy material.

To perform a diffusive electrolysis and diffuse the lithium material into the cathode 243, the cathode is rotated under 60 rpm and a direct current with current density of 0.06 A˜0.02 A per unit area of the cathode surface (cm²) is exerted on the electrolysis system at a working temperature. The lithium aluminide compound is made from the component of the electrolyte 241, lithium chloride (LiCl), and the aluminum cathode 243 by performing the diffusive electrolysis process. The interaction between the lithium and the aluminum in the electrolyte is shown as follow:

Anode: 2Cl⁻→Cl₂+2e ⁻

Cathode: Li⁺ +e ⁻→Li

The electrolyte 241 provides the lithium source from lithium chloride to form the lithium aluminide compound, and another component of the electrolyte, potassium chloride (KCL), is employed as a flux to reduce the temperature and improve the flow rate of the electrolyte.

In accordance with an embodiment of the present invention, the working temperature of the diffusive electrolysis is controlled within a range of 400° C.˜510° C. When the electrolyte is treated with the current density of 0.06 A˜0.02 A per unit area of cathode surface (cm²) and between 400° C.˜510° C. temperature at atmospheric environment, the lithium ion of the electrolyte is deposed and further diffused into the cathode 243 to form the lithium aluminide compound with high lithium content within the range of Al-2 wt. % Li˜Al-50 wt. % Li. The lithium concentration of the lithium aluminide compound is within the range of 2˜50% by weight.

Although the electrolyte includes potassium chloride as a flux, the lithium aluminide compound merely contains less than 50 ppm of potassium as a result of the poor affinity between the potassium and the aluminum cathode. Sodium is a very common impurity in chloride salt and the lithium aluminide compound contains less than 30 ppm of sodium.

Refer to FIG. 3. FIG. 3 is a sketch of X-ray crystal structures of an aluminum sheets before and after a diffusive electrolysis treatment. Portion (A) shows the X-ray diffraction pattern of an aluminum sheet (before electrolysis). Portion (B) shows the X-ray diffraction pattern of the cathode after electrolysis. A diffusive electrolysis treatment were carried out at 400° C.˜510° C., and the cathode is rotated with a speed of 2 rpm during the electrolysis. By comparing the X-ray diffraction pattern of portion (A) with portion (B), the different X-ray crystal structures of portion (B) can be identified as the X-ray pattern of Lithium aluminide (AlLi). According to the above-mentioned, the embodiment of the invention is able to make lithium aluminide compound with high lithium content in an atmospheric environment.

Although the present invention has been described in considerable detail with reference certain preferred embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A method for making lithium aluminide compound in an atmospheric environment, and the method comprising: providing an aluminum material as a cathode; dipping the cathode into an electrolyte composed of lithium chloride and potassium chloride; and exerting a direct current to the electrolyte at a working temperature and rotating the cathode with a predetermined rotating speed to perform a diffusive electrolysis, the lithium chloride of the electrolyte is decomposed and the lithium ions are reduced into lithium atoms at the surface of cathode, subsequently diffusing into the cathode to form a lithium aluminide compound during electrolysis.
 2. The method of claim 1, wherein the electrolyte essentially consists of 20˜45 wt. % lithium chloride, 30˜60 wt. % potassium chloride, and less than 5 wt. % calcium chloride.
 3. The method of claim 1, wherein the working temperature is kept within a range of 400° C.˜510° C.
 4. The method of claim 1, wherein the predetermined rotating speed is under 60 rpm.
 5. The method of claim 1, wherein the direct current is kept within a range of 0.02 A˜0.06 A per unit area of cathode surface.
 6. The method of claim 1, wherein the diffusive electrolysis uses a graphite material as an anode.
 7. The method of claim 1, wherein the composition of the lithium aluminide compound is within the range of Al-2 wt. % Li˜Al-50 wt. % Li. 